From: Mark Wilson <mwilson13@...>
Date: 2002-12-01T07:27:38+09:00
Subject: Re: Ruby ++, the one element and generators


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I can't say I really understand the extensive discussions of ++, 
although some of the explanations are sensible to the ignorant (those 
in possession of partial knowledge) -- such as the shoebox, etc.

I did read something that may be relevant in UML Distilled (2nd Ed., 
9th printing, pages 92-93), although I didn't fully understand it:

"Reference objects are things like Customer.  Here, identity is very 
important, because you usually want only one object to designate a 
customer in the real world.
...
Value objects are things like Date [Bignum, Fixnum??].  You often have 
multiple value objects representing the same object in the real world.  
For example, it is normal to have hundreds of objects that designate 
1-Jan-99.
...
Value objects should be immutable [emphasis added] ... .  In other 
words, you should not be able to take a date object of 1-Jan-99 and 
change the same date object to be 2-Jan-99.
...
In days gone by, the difference between reference objects and value 
objects was clearer.  Value objects were the built-in values of the 
type system.  [I don't understand what this sentence means.]  Now you 
can extend the type system with your own classes, so this issue 
requires more thought.  [I don't understand this sentence either, but 
it seems to suggest that the discussion of ++ involves ideas that are 
relevant to all programs, not just to the Ruby application itself.]"

Any thoughts and/or explanations would be appreciated.


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I can't say I really understand the extensive discussions of ++,
although some of the explanations are sensible to the ignorant (those
in possession of partial knowledge) -- such as the shoebox, etc.


I did read something that may be relevant in UML Distilled (2nd Ed.,
9th printing, pages 92-93), although I didn't fully understand it:


"Reference objects are things like Customer.  Here, identity is very
important, because you usually want only one object to designate a
customer in the real world.

...

Value objects are things like Date<bold> [Bignum, Fixnum??]</bold>. 
You often have multiple value objects representing the same object in
the real world.  For example, it is normal to have hundreds of objects
that designate 1-Jan-99.

...

<underline>Value objects should be immutable</underline>
<bold>[emphasis added] </bold>... .  In other words, you should not be
able to take a date object of 1-Jan-99 and change the same date object
to be 2-Jan-99.

...

In days gone by, the difference between reference objects and value
objects was clearer.  Value objects were the built-in values of the
type system.  <bold>[I don't understand what this sentence
means.]</bold>  Now you can extend the type system with your own
classes, so this issue requires more thought.  <bold>[I don't
understand this sentence either, but it seems to suggest that the
discussion of ++ involves ideas that are relevant to all programs, not
just to the Ruby application itself.]</bold>"


Any thoughts and/or explanations would be appreciated.



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